1. Field of the Invention
This invention relates to electronic musical tone synthesis and in particular is concerned with the simultaneous generation of a multiplicity of tone families each having a different number of spectral harmonics.
2. Description of the Prior Art
One of the system parameters specified in the design of an electronic musical instrument is the maximum number of spectral harmonics to be associated with each preselected tone. Usually this number is specified as the maximum number of harmonics for a tone produced at an 8-foot tone pitch. The 8-foot pitch is the nominal pitch such that the note A4 at an 8-foot pitch has a fundamental frequency of 440 Hz.
The maximum number of harmonics is an inportant and sensitive system parameter for tone generators of the class given the generic name of "harmonic synthesis" systems. Examples of systems in this generic class are described in U.S. Pat. No. 3,809,786 entitled "Computer Organ" and U.S. Pat. No. 4,085,644 entitled "Polyphonic Tone Synthesizer." In harmonic synthesis tone generation systems, the maximum number of harmonics influences the required computational speed and the number of data words that must be stored in a plurality of registers. An increase in the maximum number of harmonics must be accompanied by an increase in the computational speed and by an increase in the number of data words that must be stored. A large maximum number of harmonics can easily force the system into computational speeds that cannot be readily accomodated by low cost state-of-the-art electronic circuits.
A musical tone generation system that is implemented to generate a set of tones all having the possibility of using the maximum number of harmonics can be an inefficient system. For example, in an electronic organ voiced for playing popular music, almost all the selected tones usually have no more than 16 harmonics. The one exceptional tone class is the string tone. A "good" string tone can advantageously use a maximum of 32 harmonics. A maximum of 16 harmonics for non-string tones is adequate and is far more than is needed for tone classes such as the flutes and diapasons.